Engine ignition systems may include a spark plug for delivering an electric current to a combustion chamber of a spark-ignited engine to ignite an air-fuel mixture and initiate combustion. Based on engine operating conditions, spark plug fouling can occur wherein a firing tip of the spark plug insulator becomes coated with a foreign substance, such as fuel, oil, or soot. Once fouled, the spark plug may be unable to provide adequate voltage to trigger cylinder combustion until the spark plug is sufficiently cleaned or replaced. For example, the spark plug may be cleaned by burning off the soot accumulated on the fouled spark plug by operating the engine in speed-load conditions that sufficiently raise the spark plug tip temperature.
One example approach for spark plug cleaning is shown by Glugla et al in U.S. Pat. No. 8,132,556. Therein, based on the severity of the spark plug fouling, progressively aggressive actions are taken to burn off the accumulated soot. In particular, spark plug tip temperature is raised using a combination of spark timing advance, increase in engine load, increase in engine speed, etc.
However, the inventors herein have identified potential issues with such an approach. As one example, spark plug fouling may occur while the engine is still at an assembly plant, before vehicle delivery to a customer. At the assembly plant, the vehicle may be started multiple times for short durations due to the vehicle being moved around to multiple stations or lots. In addition, the vehicle may be started intermittently to test out engine components. The frequent, short engine operation may generate excess soot, which can accumulate on the spark plug. However, since the engine is not operated sufficiently long in speed-load regions that allow the spark plug to be warmed, the accumulated soot is not sufficiently burned off, resulting in spark plug fouling. The cooler spark plug tip temperatures can exacerbate the spark plug fouling issue. As a result, when the vehicle leaves the assembly plant, the spark plug may be fouled or prone to fouling. As such, a fouled spark plug can make the engine more difficult to start. In addition, the fouled spark plug can result in low mile warranty issues.
In one example, the issues described above may be addressed by a method for controlling fuel injection to an engine via a direct injector (DI), comprising, operating an engine with a first direct injection fueling strategy including single direct injection during the intake stroke on an engine start when in a pre-delivery state, and operating the engine with a second, different direct injection fueling strategy including split direct injection on the engine start when in a post-delivery state. In this way, in engines configured with only DI, soot fouling of spark plugs of a green engine can be reduced. However, in engines configured with both DI and port fuel injectors (PFI), fuel may be injected to the engine via the port injector while priming the direct injection fuel rail when the engine is in the pre-delivery state. Thus, by injecting via only port injection and priming a direct injection fuel rail, a priming time required is reduced and a time a vehicle spends at a plant after being assembled can be reduced. In this way, pre-delivery state fueling strategies may be adjusted based on fueling capabilities of the engine system. As one example, following vehicle assembly in an assembly plant (e.g., where the engine is green and in a pre-delivery state), the vehicle may be moved to a station where the engine is to be started for a first time (that is, a very first combustion event of the engine is commanded with no prior combustion event in the engine, the very first combustion event commanded on a very first start of the engine since initial vehicle assembly). At that station, on the very first combustion event, the engine may be fueled using a first direct fueling strategy that includes single intake stroke direct injection. Additionally, the timing of the intake stroke injection may be advanced so that the intake injection occurs earlier in the intake stroke of the first combustion event. This ensures that there is sufficient time for the fuel and air to mix thoroughly before the spark event, thereby reducing rich fuel pockets in the chamber, which could otherwise foul the spark plug. The single intake stroke direct injection may optionally be continued for a first number of combustion events since the very first combustion event of the green engine, or for a first number of starts since the very first engine start since vehicle assembly. After the first start (or first number of starts), or once the engine has left the assembly plant (e.g., delivered to the customer or dealership), when the engine is in a post-delivery state, the engine may be fueled using a second, different fueling strategy. Therein, during an engine start, the engine may be fueled via direct injection on a first combustion event, wherein the direct injection strategy includes a first intake stroke injection followed by a second compression stroke injection. In addition, the split direct injection may include one or more lean injections during the intake stroke and one or more rich injections during compression to make air fuel ratio locally near the plug richer than the overall mixture. By splitting the direct injection in the post-delivery state of the engine, the catalyst light-off temperature can be raised without increasing exhaust particulate matter emissions and degrading engine combustion stability.
In this way, a fueling strategy may be adjusted in DI-only systems when the engine is in a pre-delivery state. The technical effect of using a single intake stroke direct injection fueling strategy wherein the timing injection is advanced during engine pre-delivery state is that sufficient time may be provided for mixing the injected fuel with air in the cylinder before a cylinder spark event. As a result, there may be fewer pockets of rich combustion, and hence reduced soot emissions, despite the occurrence of multiple engine operations of short duration. By reducing soot emissions, the likelihood of spark plug fouling is reduced. However, in engine systems configured with both DI and PFI capabilities, fuel may be delivered via PFI during pre-delivery and then transitioned to DI post-delivery. In this way, fueling strategies may be adjusted based on fueling capabilities of the engine system. Overall, engine component life may be enhanced and warranty issues may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.